1. Field of the Invention
The present invention relates to a camera capable of sensing a film jam.
2. Description of the Related Art
A well-known type of patrone is loaded in a camera in a state where the leading end (leader) of a film protrudes therefrom. In general, when the patrone is set in a patrone chamber, the leader is drawn out to a take-up spool and a rear cover of the camera is closed, automatic loading of the film is started to take up the film. At this time, if the amount of the leader to be drawn out is too large or too small, automatic loading ends in failure, or the film is inadvertently overdrawn and exposed to light. Furthermore, when prints are obtained from an exposed and developed film (negative or positive), particularly by an automatic printing machine, they may be contrary to the intention of the photograph since the photographing conditions are not known to a photo laboratory.
Accordingly, there has recently been proposed a new type of film and film cartridge.
FIG. 3 is a perspective view showing a cartridge chamber 14 of a camera using such a film, and a cartridge 10. A leading portion (leader) of the film is completely wound in the cartridge 10 without protruding outside. When the cartridge 10 is inserted in the cartridge chamber 14 of the camera, a cover (not shown) of the cartridge chamber 14 is closed for shading.
FIG. 6 is a perspective view showing the states of the cartridge 10 and the film inside the camera. Numerals 13, 19a, 19b . . . 21a, and 16 to 18 respectively denote a film, perforations previously provided on the film, and frame areas to be exposed which are so defined corresponding to two perforations as illustrated that an image is formed therein. The film leader does not protrude from the cartridge 10 before loading as shown in FIG. 3. When the cartridge 10 is loaded in the camera, a fork 15 is rotated by a motor in an extruding direction (in the clockwise direction in FIG. 3) to rotate a spool 23 in the cartridge 10, by which the film 13 is extruded from the cartridge 10. This motion for extruding the film 13 from the cartridge 10 is referred to as "thrusting". Areas 24 to 26 capable of magnetic recording are provided for their respective frames, and can record in the exposed frame which the type of light source, exposure value, the date and the like.
This type of cartridge is provided with a disc, referred to as "data disc", on which the type of the film, the number of frames to be exposed and the ISO speed are recorded in a bar code. FIG. 4 is a plan view of a data disc 22, and FIG. 5 is a longitudinal sectional view of a part of the cartridge 10 adjacent to the data disc 22. The data disc 22 is fixed on the spool 23 to rotate in a one-to-one relation to the rotation of the spool 23. A photoreflector 3 is placed at a position shown in FIG. 5, and information on the data disc 22 is read based on signals from the photoreflector 3 while rotating the fork 15 in the rewind direction.
The use of the above-mentioned type of film eliminates the disadvantages of the prior art.
When the cartridge is loaded in the camera, the film wound in the cartridge is thrust and slid between a pressure plate and a guide rail. The film leader, which has reached the take-up spool in the camera, is wound on the take-up spool and the film is taken up in correlation to the rotation of the take-up spool. This automatic loading ends in response to sensing of the first frame. During thrusting, the film may be caught somewhere (referred to as "jammed"), which results in loading failure.
U.S. patent application Ser. No. 670278/1991, now U.S. Pat. No. 5,521,667, suggests reducing the time taken to recover from loading failure by detecting a jam from the change in film transport speed by using a film transport speed detector located near an aperture, once rewinding the film when the jam occurs while the film is being thrust, and restarting thrusting of the film before the film is completely wound in the cartridge.
However, realization of the above suggestion requires the film transport speed detector, which increases the size and cost of the camera.